For example, Japanese Patent Application Publication No. 2009-230921 (hereafter “Document 1”) discloses a prior art of electromagnetic opening/closing device. In the device described in Document 1, a relay unit (an electromagnetic relay) is put in a case made from synthetic resin, and a pair of main terminals and a pair of coil terminals are protruded from the case. The pair of main terminals is connected to contacts of the relay unit, and the pair of coil terminals is connected to a coil for an electromagnet of the relay unit. In addition, the pair of main terminals is connected to a power supply line from a power supply to a load(s). The relay unit (the electromagnetic opening/closing device) is turned on when an excitation current flows between the pair of coil terminals, while the relay unit (the device) is turned off when no excitation current flows between the pair of coil terminals. That is, the electromagnetic opening/closing device is turned on, thereby closing the power supply line from the power supply to the load, while the device is turned off, thereby opening the power supply line.
In such electromagnetic opening/closing devices, malfunction of contacts (a stationary contact and a moving contact) such as contact wear, contact weld or the like may occur resulting from aged deterioration, usage count (the number of times of opening/closing).